Luma13 is offering protective stickers for a number of Apple's portable devices, including the iPad mini and iPhone 5. LumaGuard for iPad mini ($24+) is a single sheet that covers 90% of the device's aluminum. It comes in a range of colors, including clear, matte, and reflective aluminum white. We found our first installation somewhat difficult, as the shape of the sticker doesn't really provide a way to line it up. This left many air bubbles that…